To celebrate its 50th birthday, Horizon invites the public to play a role in tackling the greatest challenges facing science today. This special episode of Horizon launches the £10 million Longitude Prize 2014 - a prize developed by Nesta, with Technology Strategy Board as funding partner, to find solutions to a new scientific challenge. The Longitude Prize 2014 commemorates the 300th anniversary of the original Longitude prize - a £20,000 reward for finding a way to determine longitude at sea accurately. The prize was overseen by the Board of Longitude, comprising the scientific, political and naval leaders of the day. A range of possible methods were developed with the Board of Longitude's support, but Yorkshire clockmaker John Harrison was the biggest winner with his marine chronometer clock, which enabled ships accurately and reliably to determine their longitude, avoiding potential shipwreck and enabling Britain's global trade to flourish. Horizon explores six potentia